PhD Final Exam – Pedram Payandehnia

Power Efficient Architectures for Low Noise Switched-Capacitor Filters and High Accuracy Analog-to-Digital Converters

Filters and data converters are key analog-and-mixed-signal (AMS) building blocks in communication systems, such as software-defined radios and internet-of-things. In this dissertation, novel switched-capacitor filters and analog-to-digital converter (ADC) circuit configurations have been explored which are power efficient and are digital scaling friendly. First, a novel switched-capacitor low-pass filter architecture is presented. In the proposed scheme, a feedback path is added to a charge-rotating real-pole filter to implement complex poles. The selectivity is enhanced, and the in-band loss is reduced compared with the real-pole filter. The output thermal noise level and the tuning range are both close to those of the real-pole filter. A fourth-order filter prototype was implemented in a 180-nm CMOS technology. The measured in-band loss is reduced by 3.3 dB compared with that of a real-pole filter. The sampling rate of the filter is programmable from 65 to 300 MS/s with a constant DC gain. The 3-dB cut-off frequency of the filter can be tuned from 0.490 to 13.3 MHz with over 100-dB maximum stop-band rejection. The measured in-band third-order output intercept point is 28.7 dBm, and the averaged spot noise is 6.54 nV/Hz. The filter consumes 4.3 mW from a 1.8 V supply. Next, an opamp-free noise shaping successive-approximation register (SAR) ADC is presented. Third-order noise shaping is achieved by implementing a second-order passive filter and a passive error feedback topology. In the proposed scheme, the SAR error signals (including quantization noise, comparator thermal noise, and DAC settling error) are subjected to third-order noise shaping. Therefore, the thermal noise specifications of the comparator can be relaxed. Also, since no active element is used, the proposed scheme achieves a higher power efficiency than earlier SAR ADCs. Finally, a novel 0-2 Multi Stage Noise Shaping (MASH) ADC is presented. The first stage is implemented using a 4-bit SAR ADC. The second stage uses a VCO-based quantizer (VCOQ). Unlike earlier VCOQs which provide first-order noise shaping, the proposed VCOQ achieves second-order noise filtering. To implement this noise shaping, the quantization noise of the VCOQ is extracted as a pulse-width-modulated (PWM) signal, and it is fed back to the VCO input using a charge pump circuit. Any error related to the charge pump circuitry will be first-order shaped at the output. Simulation results confirm the second-order noise shaping of the output of the ADC, and an excellent (14-bit SNDR) performance with oversampling ratio (OSR) of 16.